Question

所以我在Node中有以下代码结构：

async.parallel({
   firstTask: function firstTask(callback) {
      var firstCall = makeNetworkCall();
      callback(null, firstCall);
   },
   secondTask: function secondTask(callback) {
      var secondTaskInputArguments = [1, 2, 3, 4, 5];
      // want to make five parallel network calls to the same endpoint,
      // with each one of these five network requests
      // taking an item from the above list as input
   } 
},
function handler(err, results) {
    var firstCallResults = results.firstCall;
    // want to also grab five results from five parallel network calls in secondTask
});

在我的secondTask中，我想向第二个端点发出五个并行请求。最好的方法是什么？我可以嵌套async.parallel个调用（即在第二个任务中调用async.parallel），但这会变得混乱。我也可以将五个并行调用放在外部async.parallel中，但也很麻烦。完成这样的事情的首选方法是什么？（也许语法不同？）

Answer 1

使用async.forEach。既然你有一个参数数组，这就是它的完美案例！ async.forEach在数组中的每个元素上调用提供的函数，并在调用这些函数的每个回调后回调一次。请注意，传递给async.forEach回调的任何错误都会导致它执行其回调代码。

async.parallel({
   firstTask: function firstTask(callback) {
      var firstCall = makeNetworkCall();
      callback(null, firstCall);
   },
   secondTask: function secondTask(callback) {
      var secondTaskInputArguments = [1, 2, 3, 4, 5];
      async.forEach(secondTaskInputArguments, function secondTaskApiCalls(input, callback) {
         // do a thing for each input
         callback(null, response)
     }, function allDone(err, result) {
         // do a thing with all the results
         // this is called once all results are in OR if err is ever passed 
         // as a truthy value
         callback(null, processedResults)
     })
   } 
},
function handler(err, results) {
    var firstCallResults = results.firstCall;
    // want to also grab five results from five parallel network calls in secondTask
});

嵌套async.parallel调用？

1 个答案: